Vacuum cartridges are formed by an enclosure, in the majority of cases made of ceramic, of general cylindrical shape and closed by two end-plates inside which a stationary contact and a contact called movable contact are housed. This movable contact can be moved between a position in which the two stationary and movable contacts are touching one another so as to enable the current to flow and an open contact position in which these two contacts are separated so as to interrupt the current.
These cartridges can also comprise dielectric shields fitted around the contacts or fitted at the top and bottom parts of said cartridge.
Fixing of the dielectric shields on the enclosure, around the contacts, can be performed in several ways:
Cartridges formed by an enclosure made up of two cylindrical parts are for example known. The dielectric shield is formed by a cylindrical part comprising an annular rib extending perpendicularly to the axis of the cylinder and interposed between said cylindrical parts and the enclosure. The drawback of this solution lies in the bi-ceramic nature of the cartridge.
A cartridge called mono-ceramic is also known, comprising a monoblock enclosure the inside surface whereof presents a boss designed to cooperate with an annular recess provided on the outside surface of the shield. This solution presents the drawback of requiring machining of the enclosure.
A mono-ceramic cartridge is also known as described in the Patent U.S. Pat. No. 6,417,473 comprising a groove provided in the inside surface of the ceramic enclosure and designed to house a bungee spring which is secured vertically when inserted in the opening of the ceramic. In this embodiment, the dielectric shield is of cylindrical shape and comprises a cylindrical rib whereby the shield presses on the above-mentioned spring, welding being performed to fix the shield in definitive manner on the spring. The drawbacks of this embodiment lie mainly in the fact that the shield is not secured in rotation and that the ceramic enclosure requires machining.
Centering and welding of the respectively top and bottom dielectric shields require specific tooling and are performed at the time the cartridge is closed.
The contact pads are generally welded onto the electrodes before closing of the cartridge is performed, which means that the phases respectively of welding and of closing have to be performed in two separate steps.